An engine may be automatically stopped during selected operating conditions to conserve fuel. Stopping the engine ceases fuel flow to the engine, thereby reducing fuel consumption and engine emissions. For example, the engine may be automatically stopped when a requested engine torque is less than a threshold level, a brake pedal is depressed, and while vehicle speed is zero. Further, the engine may be automatically stopped even though there is no direct operator request to stop the engine via a dedicated engine stop or start input (e.g., an input that has a sole purpose of starting and/or stopping the engine). The engine may be automatically stopped via stopping fuel flow and/or spark to the engine. Further, the engine air inlet throttle may also be closed in response to an engine stop request so as to reduce engine noise and vibration.
The engine stopping process may occur over several seconds when cylinders that have received fuel prior to an engine stop request are allowed to combust the fuel before the engine stops. Additionally, it can take two or more revolutions of the engine for the engine to run down and reach zero speed after fuel and/or spark delivery to engine cylinders is ceased. During the engine run down (e.g., the period where engine speed decreases in the absence of combustion after an engine stop request), it is possible for operating conditions to change such that it is no longer desirable to stop the engine. For example, a driver may release a brake pedal after the engine stop request is issued, thereby indicating the driver's desire or intent to proceed to accelerate the vehicle. Fuel and spark delivery to the engine may be resumed upon the change in operating conditions. However, it may be difficult to restart the engine if engine speed decreases too rapidly during the engine restart process. Further, the engine may have to be restarted via a starter motor if engine speed decreases at a higher rate than is desired.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating an engine, comprising: adjusting an actuator a first time to automatically stop an engine; adjusting the actuator a second time before the engine reaches zero speed in response to a request to restart the engine; and adjusting an air inlet throttle position in response to a state of an intake valve and the request to restart the engine.
By adjusting a position of an air inlet throttle in response to a state of an intake valve and a request to restart an engine, it may be possible to restart the engine without causing the engine to decelerate more than is desired. For example, after combustion in a cylinder has been stopped in response to an engine stop request, it may be possible to select a cylinder in which combustion is to be reinitiated. The air inlet throttle may be opened at a time after an intake valve of a cylinder preceding the selected cylinder in order of combustion closes. In this way, an amount of air entering the preceding cylinder may be maintained at a low level so that compression torque of the preceding cylinder is low and does not cause the engine to decelerate more than is desired.
The present description may provide several advantages. Specifically, the approach may allow a driver to launch a vehicle sooner. Additionally, the approach may reduce engine fuel consumption and emissions since less fuel may be injected to restart the engine. Further, the approach may reduce engine noise and vibration since the approach increases cylinder air amount in cylinders where combustion takes place and not in cylinders where combustion is inhibited.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.